High frequency circuits used in high frequency bands are composed of circuit elements, for example, semiconductor elements, capacitors, coils or strip lines, and are stored in an internal space in a high frequency package device.
The internal space of the high frequency package device corresponds to a sort of cavity in an electromagnetic field. Therefore, it has a resonant frequency dependent on the width of the internal space. A high frequency circuit provided in an internal space is usually used in a frequency band different from the resonant frequency dependent on the internal space width. For example, a resonant frequency dependent on the internal space width is made higher than the frequency used for the high frequency circuit.
Meanwhile, high frequency circuit stored in high frequency package device has increased in its output power in recent years. With increasing of the output power, number of circuit elements is apt to increase and thus the width of internal space is apt to increase. When the width of the internal space increases, the resonant frequency decreases. As the result, the resonant frequency and the frequency used for the high frequency circuit are getting closer, and thus electric characters of the high frequency circuit degrades.
In the conventional high frequency package device, a space is divided into two by a separation wall, for example, to make the resonant frequency high when the internal space is very wide, in order to solve the above-mentioned problems (See the Japanese published Patent Application H5-83010). Alternatively, a height of the internal space is made large with a lid composing the resonant frequency being placed at high position (See the Japanese published Patent Application 2000-236045).
However, the method of dividing the internal space with the separation wall sometimes has a drawback that the side wall composing the internal space and the separation wall have different heights resulting in a gap generated at the junction portion between the lid closing an opening of the side wall and the separation wall. Thus, a waveguide mode is generated to degrade electric characteristics of the high frequency package device. On the other hand, the method of increasing the height of internal space has another problem that the height of the package becomes several times as high as an original one if the resonant frequency is required to be changed in sufficient amount, because a degree of the changing the resonant frequency become small as the height of internal space becomes higher.